Method of producing a luminescent-screen structure including light-emitting and light-absorbing areas

ABSTRACT

A METHOD INCLUDING COATING ON A SUPPORT SURFACE A PATTERN OF DEPOSITS COMPRISED OF FILM-FORMING BINDER MATERIAL CONTAINING PHOSPHOR PARTICLES; ELECTROLESSLY PLATING ONLY THE UNCOATED SURFACE AREAS BETWEEN THE DEPOSITS WITH AT LEAST ONE METAL OF THE GROUP; NICKEL, COBLAT, AND COPPER; AND THEN CHEMICALLY CONVERTING THE PLATED METAL TO A DARK-COLORED COMPOUND MATERIAL.

Aug. 1, 1972 N. FELDSTEIN 3,

METHOD OF PRODUCING A LUMINESCENT-SCREEN STRUCTURE INCLUDING LIGHT'EMITTING AND LIGHT-ABSORBING AREAS Filed May 5, 1970 V/// 1 IQ f .Z

v LYVENTOR. /V47'//4A/ fizwrm United States Patent Gfice 3,681,110 Patented Aug. 1, 1972 US. Cl. 117-335 CM 6 Claims ABSTRACT OF THE DISCLOSURE A method including coating on a support surface a pattern of deposits comprised of film-forming binder material containing phosphor particles; electrolessly plating only the uncoated surface areas between the deposits with at least one metal of the group: nickel, cobalt, and copper; and thenchemically converting the plated metal to a dark-colored compound material.

BACKGROUND OF THE INVENTION This invention relates to a novel method of producing a luminescent screen including a light-absorbing matrix for an image reproducer, such as cathode-ray tube. Color television picture tubes which include a light-absorbing matrix as part of the luminescent screen structure in substantially the same plane as the light-emitting patterns have been described previously, for example, in US. Pats. Nos. 2,842,697 to F. J. Bingley and 3,146,368 to J. P. Fiore et al. These patents describe color television picture tubes of the aperture-mask type (also called shadow-mask type) in which a light-absorbing matrix is located on the inner surface of the faceplate of the tube. In that structure, the matrix has a multiplicity of holes therein, each phosphor dot of the luminescent screen filling one hole of the matrix.

Numerous methods have been suggested for preparing the light-absorbing matrix either before or after the phosphor dots have been applied to the support surface. All of the prior methods require at least one photographic exposure in addition to that which is required to deposit the phosphor dots. While photographic methods produce usable structures, it is desirable to provide a method which avoids photographic exposures and the process controls required to carry them out satisfactorily.

SUMMARY OF THE INVENTION The novel method comprises coating a screen support surface with a pattern of deposits comprising film-forming binder material containing phosphor particles in the desired light-emitting pattern; electrolessly plating only the uncoated surface areas between the deposits with at least one metal of the group consisting of nickel, cobalt, and copper; and then chemically converting the plated metal to a dark-colored compound material.

In a preferred embodiment of the novel method, an initiator for electroless plating is adsorbed to the inner surface of the glass viewing window of a cathode-ray tube. Then, the dot patterns of blue-emitting; green-emitting, and red-emitting phosphors are deposited with a polymeric binder in any known way, leaving uncoated surface areas between the dots. Using the dots as a stencil, only the uncoated surface areas are electrolessly plated with cobalt metal. Then, the structure is processed in the usual way including baking the structure at about 440 C. in air, during which organic material is removed and the cobalt metal is oxidized to substantially black cobalt compounds.

.An advantage of the novel method is that no photographic exposures are required for making the light-absorbing matrix. This results from the fact that the pattern of the matix is defined by the pattern of the electrolessly plated metal which, in turn, is defined by the pattern of the previously-deposited phosphor-containing coated areas. Phosphor particles in the coating remain substantially undegraded by the electroless plating process.

B'RlfElF DESCRIPTION OF THE DRAWING FIGS. 1(a) to Me) are a progression of sectional elevational views of a fragment of the viewing window of a cathode-ray tube illustrating the steps in a preferred embodiment of the novel method.

FIG. 2 is a plan view of the structure shown in FIG. 1(e) from the front of the viewing window in the direction shown by the arrows 2-2.

DESCRIPTION OF THE PREFERRED EMBODIMENT An example of the novel method is now described with reference to FllGS. 1(a) through 1(e). Start with a faceplate panel for a shadowmask type color-television picture tube comprised of a viewing window 21, a fragment of which is shown in FIG. 1(e). The inner surface 23 of the window 21 is carefully cleaned to remove dirt and other foreign matter. The surface is then washed with a 10% aqueous solution of fluoroboric acid for at least one minute to leach the surface and render it hydrophilic. The surface is now rinsed with an aqueous acid stannous chloride solution to adsorb stannous ions to the leached surface. The surface 23 is now rinsed with water to remove excess stannous chloride and then rinsed with an aqueous acidic palladium chloride solution and then rinsed with water. Palladium ions replace adsorbed stannous ions on the surface 23 and are reduced to palladium nuclei, shown as layer 25 of FIG. 1(b). The layer 25 of palladium nuclei is believed to be discontinuous because the amount of adsorbed palladium present is less than is necessary for a monolayer thickness of nuclei. The amount of palladium nuclei, however, is sufiicient for initiating electroless plating of cobalt in a subsequent step.

Now, green-emitting phosphor dots 27, blue-emitting phosphor dots 29, and red-emitting phosphor dots 31 are deposited by direct photographic printing upon the treated surface 23, as shown in FIG. 1(c). Specifically, a layer of dichromated polyvinyl alcohol binder containing particles of blue-emitting phosphor is coated over the treated surface, as by slurry coating, and then exposed to a light pattern, as by projection of light through the shadow mask of the tube from a small area light source at a tfirst location. The light pattern exposes dot-shaped areas 27 of the coating, rendering the areas insoluble in water. The coating is then developed by rinsing with water to remove the unexposed coating, leaving a pattern of dots comprised of insolubilized binder containing blue-emitting phosphor particles. The process is repeated substituting a green-emitting phosphor for the blue-emitting phosphor, and exposing the coating from a small area light source at a second location so that, after developing, a pattern of dots 29 remains on the surface 23 comprised of insolubilized binder containing green-emitting phosphor particles. The process is again repeated substituting red-emitting phosphor particles for the blue-emitting phosphor particles and exposing the coating from a small area light source at a third location so that, after deevloping, a pattern of dots 31 remains on the surface 23 comprised of insolubilized binder containing red-emitting phosphor particles.

With the patterns of dots 27, 29 and 31 acting as a stencil, the surface 23 is electrolessly plated with a layer 33 of cobalt metal. The cobalt metal plates only the areas between the dots, as shown in (FIG. 1(d), because the initiator (palladium nuclei) is not covered in the areas between the dots. The electroless plating may be achieved by contacting the treated surface 23 with an aqueous solution containing, per liter, 50 grams 70 grams sodium pyrophosphate, 1.5 grams dimethylamineborane, and 7.5 ml. concentrated ammonium hydroxide. The pH is about 10.0 to 10.5, and the temperature of the solution is held at about 90 to 100 F. The normal rate of deposition is about 0.05 mil of thickness per hour. in this example, the plating is continued for about 6 minutes to deposit about 0.005 mil thickness of cobalt minimum by electroless plating.

The plating solution is removed, and the plated structure is rinsed with water and dried. The structure is now filmed and aluminized and then baked at about 440 C. in air. During the baking, organic material is removed by volatilization and oxidation. Also, the plated cobalt metal is oxidized to a substantially black compound material which contains one or a mixture of cobalt oxides. The finished product, a fragment of which is shown in FIGS. 1(a) and 2, is comprised of a glass support 21 carrying patterns of phosphor dots having a substantially black matrix 35 in the spaces between the dots 27, 29 and 31. The initiator layer 25 remains there and has a little or no effect in the operation of the tube since it is less than a monolayer thick and is completely transparent to the viewer.

GENERAL CONSIDERATIONS There are numerous variations to the novel method which do not depart from the spirit of the invention. Briefly, the novel method involves (A) treating the support surface to provide nuclei for initiating electroless plating, (B) screening a pattern of deposits of phosphorbinder on the treated surface to provide light-emitting areas and to provide a mask or stencil for the subsequent selective deposition of metal by electroless plating, (C) electrolessly plating the metal in the areas between the deposits of phosphor-binder, and then (D) converting the plated metal to a dark-colored compound material.

The electrolessly plated metal may be any one of copper, cobalt, or nickel; or combinations of these metals; or combinations of one or more of these metals with other metals such as iron, manganese and tungsten. Any metal or combination of metals which can be deposited electrolessly and can be converted to dark-colored compound material may be used. Steps (A) and (C) are obviously related and can be practiced, for example, according to the disclosures in U.S. Pat. No. 2,968,578 to J. M. Mochel and 3,446,657 to W. N. Dunlap, Jr., et al.

The screening of the pattern of phosphor-binder deposits, step (B), may be carried out by any of the known screen printing methods, for example, offset printing, screen printing, or photographic printing. The phosphor powder may be mixed with the binder at the time the pattern is printed, or the binder may be printed and then the phosphor powder adhered to the binder. The preferred methods employ the direct photographic printing on the inner surface of the viewing window of a cathoderay tube. The preferred methods may be practiced according to the disclosures in U.S. Pat. Nos. 3,406,068 to H. B. Law, 3,364,054 to M. R. Weingarten, and 3,269,838 to T. A. Saulnier, for example.

The conversion of the electrolessly plated metal to a dark-colored compound material, step (D), may be carried out by oxidizing or sulfurizing or otherwise converting the metal to a metal compound or mixture of compounds whose overall visual appearance is dark colored, and preferably black. Nickel and cobalt are known to form black oxides and sulfides. Nickel is known to form green oxides also. In some cases, however, the baking of nickel sulfide in air produces a light-colored compound. Copper is known to form black sulfides and red oxides. All of the metals mentioned are capable of forming dark-colored compound material; that is, one or a mixture of compounds, by chemical conversion from the metal. The conversion may be effected by baking in a suitable gas ambient or by chemical reaction in a liquid medium.

After preparing the luminescent pattern and light-absorbing matrix, the screen structure may be processed in the usual way to apply a reflective metal layer on top of the phosphor dots 27, 29 and 31 and the matrix 35. A suitable process for filming and aluminizing is described in an article entitled, Emulsion Filming for Color Television Screens, by T. A. Saulnier, Jr., in Electrochemical Technology, 4, 31-34 1966). Then, the aluminized screen structure is baked and assembled with the aperture mask into a cathode-ray tube in the usual way.

In practicing the novel method, the following observations were made which bear on the art of practicing the invention:

(1) Operation of the plating bath at room temperature may result in nonuniformities in induction time along the surface to be plated. This effect is reduced or eliminated by incfeasing the operation temperature of the plating bath to about to F. It is believed the increased temperature overcomes resistive elements along the surface.

(2) For certain critical thicknesses of plated cobalt metal, the plated metal may peel from the surface. This problem of peeling may be overcome by employing a thin layer of an additional promoter below the initiator layer 25. An additional promoter may be a layer of chemical material such as heat-treated tin oxide; or may be produced by modification of the surface as by leaching or hydration or both. Peeling may also be reduced or eliminated by reducing the internal stress of the plated metal thereby reducing the forces causing the peeling.

(3) Porosity in the phosphor dots may permit some plating nuclei to be exposed thereby permitting metal to be plated through the dots. To eliminate this tendency, the dot should exhibit the minimum porosity and have the maximum hydrophobic characteristic. These may be achieved in several ways, for example by baking the deposited dots at about C. for about 10 minutes; or by incorporating an organic filler, such as an acrylate copolymer, which imparts a greater hydrophobic character to the dots. It is believed that a film-forming binder is most effective in imparting a minimum porosity to the desired dot.

(4) The efiiciency of most phosphor particles is sensitive to the present of impurities and foreign ions. Ions of cobalt, nickel, copper, etc. frequently act as poisons when diffused into the phosphor particles. Experiments with cobalt metal have shown that the use of a film-forming binder provides suitable protection of the phosphor dots from the ions involved in the electroless plating so that the efiiciency of the phosphor particles is substantially unaffected. Again, a minimum porosity in the phosphor dot provides a greater protection against degradation of the phosphor efficiency. After the binder is removed, the phosphor particles are substantially unaffected by the matrix material during subsequent tube-making processes.

I claim:

1. A method of producing a luminescent-screen structure for a cathode-ray tube comprising (a) adsorbing to a supporting surface an initiator for electrolessly plating at least one metal of the group consisting of nickel, cobalt and copper,

(b) coating said supporting surface with a pattern of deposits comprised of phosphor particles and a filmforming binder therefor with uncoated surface areas between said deposits,

(c) electrolessly plating at least one metal of the group consisting of nickel, cobalt and copper upon said uncoated surface areas without plating metal on said deposits, said pattern of deposits acting as a stencil for plating said metal.

(d) and then chemically converting said plated metal to a dark-colored compound material.

2. The method defined in claim 1 wherein said metal is oxidized to a dark-colored compound material.

3. The method defined in claim 1 wherein said metal is sulfurized to a dark-colored compound material.

4. A method of producing a luminescent-screen structure for a cathode-ray tube comprising (a) adsorbing on the inner surface of a glass viewing window of a cathode-ray tube an initiator for electrolessly plating cobalt metal.

(b) coating said surface with a pattern of deposits comprised of particulate phosphor material and a film-forming binder therefor with uncoated surface areas between said deposits,

() electrolessly plating cobalt metal on said intermediate surface areas without plating metal on said pattern of deposits, said pattern of deposits acting as a stencil for plating said metal,

(d) and baking said plated structure in an oxidizing ambient to convert said cobalt metal to a darkcolored compound material.

5. The method defined in claim 4 wherein palladium ions are adsorbed on said surface.

6. The method defined in claim 4 wherein said adsorption is achieved by first rinsing said surface with an aqueous solution of a stannous salt and then rinsing said surface with an aqueous solution of a palladium salt.

References Cited UNITED STATES PATENTS 3,365,292 1/1968 Fiore et al. 11733.5 CMX 3,212,917 10/1965 Tsu et a1 11747 R 3,474,040 10/ 1969 Hedler et al. l17-33.5 CMX 3,269,854 8/1966 Hei 11747 RX 

